The terms “hamstring,” “hamstrings” or “hamstring muscle” are generally used to refer to the three large muscles constituting the back of the upper leg. The hamstrings serve to flex the knee joint and extend the hip. Everyday activities as well as most athletic activities involve the repetitive contraction of the hamstring muscle. The hamstring muscle tightens as a result, and requires effective stretching to retain its full range of motion. In the absence of such stretching, the tight hamstrings will have a deleterious effect on the person's skeletal alignment, typically resulting in lower back and knee pain, as well as problems with posture.
Stretching any muscle is best done at a slow rate. Attempting to quickly stretch the muscle will rouse the muscle's inherent tendency to contract when pulled, thereby resisting the sought-after lengthening of the muscle.